Manufacture of aluminium



Aug. 17, 1937. o. KRUH 2,090,451

MANUFACTURE OF ALUMINIUM File/ricky?, 1935 2 Sheets-Sheet l F352 l JVQ/Aug. 17, 1937. Q KRUH MANUFACTURE OF ALUMINIUM 2 Sheets-Sheet 2 FiledMay 29. 1935 Patented Aug. l 17, 1937 UNITED STATES PATENT OFFICEApplication May 29, 1935, Serial No. 24,023 1n Austria June 5, 1934 10Claims.

My invention relates to the production of pure aluminium by the processof reducing aluminium oxide by means of carbon or carbonaceous reducingagents at a. high temperature under certain new conditions. Experimentshave already been made to reduce aluminium oxide by carbon at a hightemperature; however, without success. It wasgfor instance, proposed toform a compressed bar of a mixture of aluminium oxide with carbon and touse this bar as an electrode in an arcdlscharge furnace in the presenceof an inert or reducing gas like nitrogen, hydrogen or carbon hydride.Trials based on this proposal failed for the reason that the gas havingno access to the inner particles of the mixture, the reaction stops atonce after reduction of the surface layer of the bar. It has furtherbeen proposed to reduce a mixture of aluminium oxide with differenthydrocarbons such as turpentine together with soot, this mixture forminga paste, and heating this mixture in a furnace in an atmosphere ofacetylene at a high temperature. The acetylene was expected to preventthe reoxidation by the air of the aluminium formed. This proposal could.25 not succeed, as acetylene decomposes at a high temperature, andforms soot which soon lls the furnace. 'I'his soot combines with thealuminium produced to form aluminium carbide. Another proposal was madeto reduce aluminium 3U oxide by carbon in vacuo at a high temperaturewith the idea that carbon monoxide, formed on account of the reaction,could be removed quickly from the reaction chamber, and that aluminiumcould be so distilled without being oxidized 3;, by the carbon monoxide.This third proposal could not succeed either, because the carbonmonoxide and the aluminium have the same weight and, therefore, the samevelocity. On account of those difficulties aluminium has hitherto 4Ubeen manufactured usually by an electrolytic process. Pure aluminiumoxide is dissolved in fused cryolite and mixture of cryolite andelectrolized. Aluminium is deposited at the cathode, and forms there aliquid which is scooped .1501i from time to time. The production of onekilogramme of aluminium requires theoretically 23.5 kwh.; in practice,however, 28-30 kwh. are consumed. This large consumption of electricalenergy in the electrolytic process has made the 5U cost of aluminiumhigh. The cost of the high current generators, the regulation of thevoltage of the bath and the necessity of using only very pure aluminiumoxide increase the cost of the aluminium further. 55 My invention hasfor its object to obviate those (Ci. 'l5-68) disadvantages, and to makethe production of aluminium simpler, and cheaper. This is possible sincethe production of one kilogramme of aluminium by the new processrequires only about 10 kwh. Thecost of the electrical energy is con- 5siderably lower as alternating current of higher voltage may be used.

According to my invention aluminium is made by the following process:Aluminium oxide is loosely mixed with a carbon containing material 10(preferably in proportions corresponding to the stoichiometricalrelation between aluminium oxide and carbon) and this mixture is heatedin a reaction chamber to a high temperature, while a continuousprotective gas flows through the 15 reaction chamber, and carries awayfrom the reaction chamber the gases formed by the reaction, mainlycarbon monoxide, and the aluminium vapour. The aluminium particles areysurrounded by the protective gas, and so protected from the 20 attackby other gases present. The mixture of gas and vapour when leaving thereaction chamber is cooled at once to a temperature at which thealuminium particles remain intact. The aluminium vapour is precipitatedto a greater g5 part on a cooling surface, while the gases pass on.'I'he precipitated aluminium is removed by mechanical means to a chamberwhere the aluminium is collected. That part of the aluminium that is notprecipitated and is carried further by the gases is partly removed fromthem by a conveyer screw, and the last traces are retained by a filter..Y

I have found that itI is advantageous to give the reaction chamber theshape of a hollow channel, and to set immediately above the reactionchamber a cooling device extending along the full length of the chamber.The cooling device consists of a rotating cylinder cooled from theinside so that the ascending aluminium vapour is precipitated on itssurface from which the aluminium is scraped ofi' by means of a scraperand removed from the furnace.

The contents of the reaction chamber may be heated in any known manner,the best method being to utilize electrical power.

The use of the hydrogen as a protective gas has given very good results,and the reaction involves an intermediate formation of acetylene.

At the high temperature of the furnace the hydrogen reacts with thecarbon to which aluminium oxide is admixed, and considerable quantitiesof acetylene are formed. 'I'he energy required for the formation ofacetylene is provided for by the heat of the furnace, since thisreaction is endothermic. This energy is by no means lost, since it isrecovered at the reduction of aluminium oxide by acetylene, the ylatterbeing a very effective reducing agent. The hydro- 5 gen of the consumedacetylene is set free and instantaneously forms with the carbon presentfresh acetylene on account of the temperature equilibrium between thehydrogen, carbon, and acetylene being aiected by the disappearance ofthe acetylene. The velocity of the reaction is further 4increased by thecircumstance that acetylene reacts more readily with aluminium oxidethan does carbon. The reduction of aluminium oxide may be attained byacetylene alone without coal; hydrogen, however, must be mixed with theacetylene in a proportion corresponding to the temperature equilibriumbetween hydrogen, carbon, and acetylene.

The amount of protective gas required for removal of the gases producedby the reaction,

especially carbon monoxide, and for the transportation of the aluminiumvapour is not great, since the molecular weight of hydrogen is small,and the average molecular velocity oi' hydrogen is much higherthan thatof carbon monoxide and that ofthe aluminium vapor, provided thecalculation of the velocities be based o'n the same temperature. Forinstance, the average velocity of the hydrogen molecules is .3.74 timeshigher than that of the molecules of the carbon monoxide, and,accordingly, the hydrogen iills the space 3.74 times more than carbonmonoxide. Therefore, by using an amount of hydrogen about twice that ofthe carbon monoxide, the space will be filled 7.48 times more byhydrogen than by carbon monoxide, and this will be suiiicient to protectthe aluminium particles from the attack by carbon monoxide, as there arealways hydrogen molecules interfering between the molecules of aluminiumand carbon monoxide.

Hydrides of carbon, or mixtures thereof may be used for the reduction ofaluminium oxide; but hydrogen must be added in the correct proportion,as otherwise soot is formed. VThe correct proportion may be determinedin advance by well-known simple preliminary, quantitative tests to thatend.

The accompanying drawings illustrate diagrammatically a device forcarrying out the process according to my invention and referringthereto:

Fig. 1 is a partly sectional side elevation, taken on lines A-A of Fig.2; Fig. 2 is a partly sectional front elevation, taken on lines B-B ofFig. 1; and Fig. 3 is a partly sectional plan view,

taken on lines C--C of Fig. 1.

In the furnace I there is provided an elongated shallow channel I whichserves as a reaction chamber for the production of aluminium.

The walls of this chamber consist of a lining 2 of ireproof material,protected from the action of excessive temperatures by the cooling tubesi3.A

The rea'ction chamber 'I communicates through a channel 6 with a top 3of the furnace, this top being provided with a rotary sieve 4 and, at aucts leaving the same, and at the same time hydrogen enters at 5 and isintroduced into the chamber' through the channel 8. Electric current issupplied to the reaction chamber by the leads 9 and the electrodes l0,provided on both sides of the chamber. By the passage ci the electriccurrent through the mixture of aluminium oxide and carbon contained inthe reaction chamber the mixture is heated to a high temperature, andinthe presence of hydrogen the reduction of aluminium oxide to aluminiumtakes place.

The protective gas ows through the reaction chamber and carries reactiongases, mainly carbon monoxide, and the aluminium vapour towards aninternally cooled rotary cylinder II, situated above and along thereaction chamber. This gaseous mixture is cooled by the cylinder to atemperature at which carbon monoxide is no longer able to oxidizealuminium. The aluminium vapour is precipitated on the surface of thecylinder to a kind of metallic snow, and is scraped oif the coolingcylinder by a movable scraper I2, and conveyed through the funnelshapedchute i3 to a cylindrical channel I8 wherefrom it is transported by aconveyor screw I4 through the discharge pipe I9 to the chamber I5 wherethe aluminium collects. The part of the aluminium not precipitated onthe cooling surface but carried further by the owing gas mixture settleson the conveyor screw I4, and the last traces of aluminium are retainedby the lter I6 in the chamber- I5. A block-shaped packing 20 interposedbetween the top of the cylinder Il and the inner Wall of the furnace lprevents the iiow ofhydrogen from shunting the reaction chamber I.

The mixture of hydrogen and carbon monoxide leaves the chamber I5 at Iland may be used, then, for any purpose. I prefer, however, to recoverthe pure hydrogen from this mixture and to reconduct it into the furnaceI in order to obtain in the device a closed circulation of theprotective gas. To this end, as shown in Fig. 1 by the dot and dashlines, the mixture of gases is passed from the chamber I5 through theconduit 2l to a device 22 wherein the hydrogen is separated from thecarbon monoxide and from other impurities, and returns to the furnacethrough the conduit 23, a pump or exhauster 24 of known constructionbeing inserted in this conduit for maintaining the required circulationof the hydrogen. Fresh hydrogen may be supplied to the furnace or may beentered into circulation by the pipe 25 or by the pipe 26. Devices forseparating pure hydrogen from a gaseous mixture containing hydrogen arewell-known in the art and their special construction does not constituteany part of my inventiongilhus by the rectangle 22 I only have indicatedwhere such a device is to be disposed without showing the known parts ofthe device.

The finely divided aluminium collected in the chamber I5 may be used inthis state for paints,

gen).A For this purpose the chamber I5 may be constructed in any knownmanner, but preferably in the manner shown in-FigI` 1 by way 0f example.In this figure the inner walls of the chamber I5 are covered with alining 21 consisting of a refractory material which does not react withmolten aluminium, for instance cryo lite, magnesite or any othersuitable stone or 5 brick, but I prefer to use sintered aluminium oxide,as this lining Y'material gives excellent results. 'I'he aluminiumcollected in the chamber I5 is melted upon a casting bed which isconstructed like a filter and consists of a perforated i bottom 28carrying a heaped layer 29 of a refractory material incapable ofreacting with the aluminium at elevated temperatures. This material maybe the same as that of the lining 21,

for instance cryolite, magnesite or the like, but i preferably sinteredaluminium oxide. To melt the aluminium any suitable heating means may be`provided for, preferably electrical means, for example a high-frequencycoil 30 arranged outside the chamber I5, as shown in Fig. 1.v Theconstruction of electrical heaters for melting and casting purposes iswell-known in the art and, therefore, does not constitute a part of myinvention. The melted aluminium passes into the bottom part of thechamber I5 through the filter 23, 29 which retains any impurities, andmay be discharged from the chamber I5 through the outlet.

The device is to be fitted with the required number vof cooling anddriving implements, it

being understood that I do not`claim the special constructions of suchimplements, since they are frequently used in metallurgical andelectrometallurgical processes. In the device illustrated by thedrawings the cylinder II, the tubes 8 and the electrodes Iii are to becooled by water during operation. For this purpose water inlet pipes 32,34, 35 and water outlet pipes 33, 35, 31 are provided for. The pipe 32projects into the interior of the cylinder II so as to discharge coolingwater thereinto. The water leaving the cylinder I I through the spout 35flows into the vessel 39 and from there into the pipe 33. The ends ofthe cooling tubes 3 are fitted into water distributing chambers 4B and4I which are connected to the pipes 34 and 35, respectively, so as topermit the cooling water to flow from 34 through 40, 3 and 4I into 35.Each electrode I0 is partly surrounded by a water-filled casing 42 whichis connected onone side to the inlet pipe 33 and on the other sideto theoutlet pipe 31.

The axles 43, 44 and 45 of the sieve 4, of the cylinder II and of theconveyor I8, respectively, are rotatably mounted in bearings 4B, 41 and48, respectively. The axles 43 and 45 are provided 5 3 with pulleys 49and 50, respectively, for being rotated by the latter with proper speed.The cylinder II isdriven by a pulley 5I which is secured to thecylindrical portion of the tube 39. Of course, the pulleys 49, 50 and 5Imay be replaced by any other driving means, for instance by electricmotor drives.

The top 3 of the furnace I may be closed by a cover plate 52 pivotedabout 53 and provided with handles 54.

What I claim is:

l. The process of manufacturing aluminium, which comprises preparing aloose mixture of aluminium oxide and carbonaceous reducing material sothat gas brought into contact with said 70 mixture has access to theinner particles thereof;

exposing said mixture to a flowing protective gas inert to aluminiumwhile heating the mixturev to a temperature suilicient to reduce thealuminium oxide by the action of the carbonaceous material and tovaporize into said protective gas the aluminium formed by reduction;carrying away the composite of aluminium vapour, protective gas, andgaseous reaction products formed during thesaid reduction process; andcooling said composite to' a temperature suillcient to transform thealuminium vaporized into the solid state and to prevent the aluminiumparticles from reacting with the said gaseous reaction products.

2. The process of manufacturing aluminium, which comprises reducingaluminium oxide by carbonaceous material in the presence of a gasmixture containing hydrogen and acetylene, said reducing process beingcarried out at a temperature sui'iicient to vaporize into said gasmixture thealuminium formed by reduction.

.3. The process of manufacturing aluminium, which comprises preparing aloose mixture 'of aluminium oxide and carbonaceous reducing material sothat gas brought into contact with said mixture has access to the innerparticles thereof; exposing said mixture to flowing hydrogen while'heating the mixture to a temperature sufficient to reduce the aluminiumoxide-by the action of the carbonaceous material and to vaporize intosaid hydrogen the aluminium formed by reduction; carrying away thecomposite of aluminium vapour, hydrogen and gaseous reaction productsformed during the said reduction process; and cooling said composite toa temperature sufficiently low to prevent the aluminium particles fromreacting with the said gaseous reaction products and to condense thealuminium vapours so as to obtain the aluminium in the solid state.

4. The process of manufacturing aluminium, which comprises looselymixing aluminium oxide and carbon; heating said mixture to a temperaturesuillcient to reduce said oxide by the action yof the carbon and tovaporize the aluminium formed thereby; rsurrounding the vaporizedaluminium particles with a protective gas inert to aluminium so as toprotect said particles from the chemical attack by other gases present;carrying away the gaseous mixture of aluminium vapour, protective gas,and reaction gases formed during the reduction process; cooling saidgaseous mixture to a temperature suillcient for preventing the aluminiumparticles from being oxidized by the said reaction gases;` and removingfrom the said gaseous mixture the aluminium in the solid state.

5. The process of manufacturing aluminium, as claimed in claim 1,wherein the aluminium oxide and the carbonaceous material are mixed inproportions corresponding to the stoichiometrical relation betweenaluminium oxide and carbon.

6. The process of manufacturing aluminium, which comprises reducingaluminium oxide by acetylene in the presence of hydrogen at a,temperature sumcient for vaporizing into said hydrogen the aluminiumformed by reduction.

7. The process of manufacturing aluminium as claimed in claim l whereinthe said protective gas contains hydrogen maintained in a proportionwhich is sufiicient to protect the aluminium particles from the attackby other gases present and to prevent the formation of aluminiumcarbide.

8. The process of manufacturing aluminium as claimed in claim 3, whereinthe amount of hydrogen supplied to the process is at least twice that ofthe carbon monoxide formed by the reduction of the aluminium oxide.

9. The process of manufacturingaluminium, which comprises reducingaluminium oxide by carbonaceous material in the presence of a gas Cilmixture containing hydrogenA and acetylene inl proportions correspondingsubstantially to the temperature equilibrium between hydrogen, car- 10minium oxide and carbonaceous material in a reaction chamber to atemperature which affords the reduction of the aluminium oxide by carbonand the vaporization of the aluminium formed thereby; supplying to saidchamber a. protective gas inert toaluminium; withdrawing from the re--action chamber the mixture of aluminium vapour,v

protective.- gas,-` and gaseous reaction products formed during the saidreduction process; lcooling 'said mixture immediately after leaving' thereaction chamber, to a. temperature sumcient to prevent oxidation o! thealuminium and formation'o!l aluminium carbide and to condense thealuminium vapour; carrying away the condensate of aluminium from thereaction chamber together 10 with 'the said gaseous mixture; andseparating from this latter the aluminium in the solid state.

OSIAS KRUH.

